Brake Line Distribution block port sizes are different

I don't understand why you are blocking off anything. If you have a dual master, it has two ports out. Each goes to one of the "in" ports on the distribution block (and they are specific -- one is for the front brakes, the other for the rear). That leaves 3 "out" ports: one for each front line, and one for the rear brakes. So what are you blocking off?

Are you trying to use the single master cylinder distribution block? I don't see how that will work. You need a dual circuit distribution block to match the master cylinder.